Segmented windings are commonly used in modern electrical machine applications, such as in hybrid-electric vehicles. These windings typically comprise a plurality of segmented conductors which include in-slot portions and ends that are connected together. The conductors are positioned in the slots of a laminated core portion of the electric machine (e.g. stator slots), and the ends of the conductors are connected to form windings for the electric machine.
Segmented conductors for electric machines are often provided in the form of U-shaped conductors which include two legs and a central U-turn portion extending between the legs. These U-shaped conductors may also be referred to herein as “U-shaped bars” or conductors with “U-turn portions”. The terms “U-shaped conductor”, “U-shaped bar” and “U-turn portion” as used herein refer to electric conductors or conductor portions where the axial direction of the conductor changes by more than 90°, such as by about 180°. However, these terms are not limited to conductors or conductor portions that form a perfect “U” shape.
U-shaped conductors are typically created by bending and twisting wire bars into U-shaped conductors with two legs and a U-turn between the legs. The two legs are separated by a given span which allows the conductor to extend across a number of stator slots by virtue of the U-turn alone. The legs of the conductors are then inserted into the slots of the core from an insertion end of the core. Following insertion of the conductors into the slots of the core, the bend portions (i.e., the U-turn portions) are positioned on one side of the core (i.e., the “insertion side”) and the leg ends extend from the other side of the core (i.e., the “connection side” or “weld side”). The legs ends may then be bent to appropriate positions, often with a first leg typically bent in one direction and another leg bent in the opposite direction such that the entire segmented extends a given slot span (e.g., 12 slots). Finally, the tips of the leg ends are connected together at the connection side of the stator to complete the windings. These connections include adjacent leg ends that are aligned directly and welded together, non-adjacent leg ends that are connected through jumper wires, and terminal connections. Together, the connected conductors form the complete winding arrangement.
Although the conductors are connected together at their ends, care must be taken to ensure that adjacent conductors do not touch each other and short-circuit the designed winding arrangement. Accordingly, electrical insulation is typically provided on the conductors to electrically insulate the conductors from one another. Segmented conductor insulation systems typically include an enamel coating that is applied and bonded directly on the bare copper wire by the wire manufacturer. Different grades of materials and temperature classes may be used for this initial layer of insulation. The electric machine manufacturer also typically applies a slot liner positioned along the walls of the slots in the lamination stack. The slot liner prevents the conductors from short-circuiting against the core.
In addition to an enamel coating on the conductors and slot liners in the core slots, some winding arrangements also include a band of insulation material on the ends of the conductor that are formed and welded together. These bands are often used in association with high voltage electric machines, such as those used with hybrid electric vehicles. In these machines, the band of insulation material often extends between adjacent layers of conductors at the insertion end or the connection end of the core. This arrangement with an additional insulation band provides extra electrical insulation protection at the U-turn portions or the connection ends of the conductors. This additional insulation protection may be significant since the welding process can sometimes thermally damage the base enamel insulation system of the wire. However, the downside to such insulation bands is that they significantly degrade the thermal performance of the end turn cooling on the weld side since the bands block the passage of cooling fluid across the surfaces of the conductor.
Accordingly, it would be advantageous to provide an insulation arrangement for electric machines with segmented conductors which provides high integrity insulation while also avoiding the thermal problem that adding insulation bands in the end turn region creates. It would be advantageous if such insulation arrangement could be provided easily and at relatively low cost to the manufacturer.